1. Field of the Invention
The present invention generally relates to an arc welding power source. In particular, the present invention relates to an arc welding power source configured to simplify the sequence of an activating signal for a crater mode and a crater repetition mode.
2. Description of the Related Art
A power source for consumable or nonconsumable electrode arc welding is equipped with a current control mode called crater mode and crater repetition mode. Details of these modes are described below.
FIG. 6 is a timing chart for illustrating the crater mode. In the figure, Graph A shows the waveform of an activating signal On supplied to the power source from outside, and Graph B shows the waveform of a current Io outputted from the power source. In an instance where a human operator manually handles the welding torch, the activating signal On corresponds to the on/off state of the torch switch. In an instance of automatic welding where a welding torch is mounted on an automatic carrier, the activating signal On is a sequence control signal supplied from a programmable logic controller (PLC).
When the activating signal On is turned on (rising to a high level) at time t1 as shown in Graph A, a predetermined start current Is is supplied, as shown in Graph B. Then, when the activating signal On is turned off (falling to a low level) at time t2, a predetermined welding current Iw is supplied. When the activating signal On is turned on (rising to the high level) again at time t3, a predetermined crater current Ic is supplied. When the activating signal On is turned off (falling to the low level) at time t4, the output current Io is terminated, and the welding is stopped.
As shown in FIG. 6, the first on-period of the activating signal On (from time t1 to t2) corresponds to a start period Ts during which the start current Is is supplied. Likewise, the off-period of the activating signal On (from time t2 to t3) corresponds to a welding period Tw during which the welding current Iw is supplied. Further, the second on-period of the activating signal On (from time t3 to t4) corresponds to a crater period Tc during which the crater current Ic is supplied. Accordingly, in order to perform the crater mode welding with the automatic welding machine, the activating signal On shown in Graph A should be produced in a control unit such as a PLC, while the welding power source is set to the crater mode.
FIG. 7 is a timing chart for illustrating the crater repetition mode. In the figure, Graph A shows the waveform of an activating signal On supplied to the power source from outside, and Graph B shows the waveform of an output current Io outputted from the power source.
When the activating signal On is turned on (rising to a high level) at time t1 as shown in Graph A of FIG. 7, a predetermined start current Is is supplied as shown in Graph B of FIG. 7. When the activating signal On is turned off (falling to a low level) at time t2, a predetermined welding current Iw is supplied. When the activating signal On is turned on (rising to the high level) at time t3, a predetermined crater current Ic is supplied. When the activating signal On is turned off (falling to the low level) at time t4; the welding current Iw is supplied again. When the activating signal On is turned on (rising to the high level) at time t5, the crater current Ic is supplied again. When the activating signal On is turned off (falling to the low level) at time t6, the welding current Iw is supplied again. Thereafter, at time t7, when the activating signal On is turned on and off twice within a relatively short period (i.e., double-clicked), the output current Io is terminated, and the welding is stopped.
As seen from FIG. 7, the first on-period of the activating signal On (from time t1 to t2) corresponds to the start period Ts. The first off-period of the activating signal On (from time t2 to t3) corresponds to the welding period Tw. Then the second on-period of the activating signal On (from time t3 to t4) corresponds to the crater period Tc. The second off-period of the activating signal On (from time t4 to t5) corresponds to a repeated welding period Tw. The third on-period of the activating signal On (from time t5 to t6) corresponds to a repeated crater period Tc. The third off-period of the activating signal On (from time t6 to t7) corresponds to another repeated welding period Tw.
The above-described crater repetition mode is often employed when a relatively large crater is created at the end of the welded portion. This is because, in the case where the crater is large, supplying the crater current Ic just once as in the crater mode shown in FIG. 6 is not sufficient for effectively filling the crater. To finish the welding work, the following process may be employed instead of the double-click in the crater repetition mode shown in FIG. 7. When manually performing TIG (tungsten inert gas) welding, it is a common practice to moves the welding torch upward off the welding spot at a desired timing after time t3, thereby forcibly extinguishing the arc to finish the welding. Alternatively, the welding may be repeated when the activating signal On is turned on for a short time after time t3, whereas the welding is terminated when the activating signal On is turned on for a longer time than a predetermined threshold.
In the crater repetition mode, as described above, it is necessary to generate a complicated activating signal On as shown in Graph A of FIG. 7 with a control unit such as the PLC. The foregoing conventional art is described in JP-A-2000-218367 and JP-A-2003-062667, for example.
As noted above, to perform welding in a crater mode or crater repetition mode with the use of a conventional arc welding power source, it is necessary to generate a complicated sequence signal, i.e. the activating signal On shown in Graph A of FIG. 6 or Graph A of FIG. 7.
In using a robot welding machine, a function equivalent to the crater mode or the crater repetition mode can be performed by adding a sequence of an output current condition to the operation program. In the case of the manual welding, on the other hand, the activating signal On is generated through manipulation of the torch switch. Thus, a manipulation error is prone to occur when the operation to be performed is complicated, and the burden imposed on the human operator tends to be heavy. For the automatic welding, the activating signal On is often generated by a general-purpose control unit such as the PLC. In this case, it is necessary to program a complicated sequence of the activating signal On, based on correct and sufficient understanding of the sequence of the crater mode or the crater repetition mode of the welding power source. In composing a program, it is necessary to adjust the start period Ts, the welding period Tw, and the crater period Tc depending on the work to be welded. Such adjustment takes a long time because optimal conditions need to be found while correcting the program for the PLC, whereby the production efficiency deteriorates.